• The suspect, Vance Luther Boelter, allegedly shot and killed Minnesota Democratic state Rep. Melissa Hortman, and her husband, Mark. He is also accused of injuring another Democratic lawmaker in the state and his wife.
• He was arrested late Sunday night after a manhunt that authorities said was the largest in state history.
• The gunman allegedly impersonated a police officer when he entered the victims' homes.

Federal prosecutors on Monday charged the man accused of assassinating a Minnesota state lawmaker and her husband, and shooting another lawmaker and his wife, with six federal counts, including stalking, murder and firearms offenses.

Vance Luther Boelter, 57, is facing both state and federal charges in the assassination of Minnesota Democratic state Rep. Melissa Hortman and her husband, Mark, and the shooting of Democratic state Sen. John Hoffman and his wife, Yvette, in a separate attack.

The details of the crime "are truly chilling. It is no exaggeration to say that his crimes are the stuff of nightmares," Joe Thompson, the acting U.S. attorney for Minnesota, said Monday.

Thompson said "it is too early to tell" whether the Justice Department will seek the death penalty in Boelter's case, but it "is one of the options for several of the charges."

Thompson said that early Saturday morning, Boelter went to the homes of four Minnesota state lawmakers "with the intent to kill them."

One of the lawmakers, a Minnesota state representative, was not home when Boelter arrived at her home, so he left, Thompson said.

The other, Minnesota Democratic state senator Ann Rest, said authorities told her Boelter had been parked near her house early Saturday morning.

"I am so grateful for the heroic work of the New Hope Police Department and its officers," Rest said in a Monday statement.

"Their quick action saved my life," she said.

Boelter "planned his attack carefully," including researching the victims and their families, and he "conducted surveillance of their homes," Thompson said.

Boelter's arrest Sunday night was the result of what authorities called the "largest manhunt" in Minnesota state history, spanning 43 hours and involving 20 SWAT teams.

Doorbell camera footage showed Boelter wearing a mask and impersonating a police officer to gain access to the victims' homes, where the shootings took place.

State officials also said Monday that they will seek first-degree murder charges against Boelter.

The maximum penalty for a conviction on first-degree murder charges is life in prison without parole, said Hennepin County Attorney Mary Moriarty.

Boelter was also carrying a list with "dozens and dozens of names" of potential targets, including some Thompson said he believed to be "abortion rights supporters."

"Obviously, his primary motive was to go out and murder people," Thompson said. "They were all elected officials. They were all Democrats."

"Beyond that, I think it's just way too speculative for anyone that's reviewed these materials to know and to say what was motivating him in terms of ideology or specific issues," he added.

U.S. Rep. Greg Landsman, D-Ohio, said in a statement later Monday that the FBI found his name among Boelter's notes during their search.

Landsman said the Capitol Police informed him of that on Sunday, while the suspect was still being sought.

"We worked very closely with the Cincinnati Police Department to arrange for increased security for my family and me," the congressman said.

FBI Director Kash Patel said his agency "stands united with our law enforcement partners to find and hold accountable anyone who commits such despicable acts," according to a statement Monday.

Attorney General Pam Bondi said that the "horrific acts of violence will not go unanswered: the Department of Justice will prosecute this suspect to the fullest extent of the law and if convicted deliver severe consequences for his alleged crimes."

Authorities captured Boelter late Sunday in a rural part of Sibley County, Minnesota, where he was found crawling in a field. He was armed at the time of his arrest, but gunfire was not exchanged at the time of his arrest, authorities said.

Earlier on Sunday, authorities said, they had discovered his car and hat in Sibley County, leading them to zero in on the area.

The shootings, which Gov. Tim Walz said appeared to be "politically motivated," have rattled Minnesota and lawmakers across the country.

"Political assassinations are rare," Thompson said Monday. "They strike at the very heart of our democracy."

This is a breaking news story and will be updated.